They are incorrect. Building luxury housing will take some of the demand pressure off of non-luxury housing (which constitutes the vast majority of the housing in San Francisco), thereby lowering its price.
The only way this wouldn't work is if nobody could afford to live in the new luxury housing. But we know for sure that there are plenty of people who want to, can afford to, and are moving into the newer luxury developments as soon as they are available. The lower-quality housing those people move out of is now available for people who can't afford the new luxury housing.